Premixing burner and method for operating a premixing burner

ABSTRACT

A method for operating a premixing burner is provided. The premixing burner includes a premixing zone. An air mass flow and fuel may be injected into the premixing zone, and a potential hot gas backflow area may form. A fluid containing no fuel is injected downstream from the fuel injection into the premixing zone in order that a hot gas backflow area does not form. A premixing burner including a premixing zone is also provided.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the US National Stage of International Application No. PCT/EP2008/059658, filed Jul. 23, 2008 and claims the benefit thereof. The International Application claims the benefits of European Patent Office application No. 07014820.0 EP filed Jul. 27, 2007. All of the applications are incorporated by reference herein in their entirety.

FIELD OF INVENTION

The present invention relates to a premixing burner, especially a syngas premixing burner, and to a method for operating a premixing burner.

BACKGROUND OF INVENTION

Premixing burners typically comprise a premixing zone in which air and fuel are mixed before the mixture is directed into a combustion chamber. The mixture burns in said chamber, with a hot gas under increased pressure being generated. The hot gas is transferred on to the turbine. The primary consideration when operating premixing burners is to keep nitrous oxide emissions low and to avoid a flame blowback.

Syngas premixing burners are characterized by syngases being used as a fuel in them. Compared to the classical turbine fuels of natural gas and oil which essentially consist of hydrocarbons, the combustible elements of the syngases are essentially carbon monoxide and hydrogen. Depending on the gasification method and the overall plant concept, the heating value of the syngas is around 5 to 10 times smaller than that of natural gas.

As well as the stoichiometric combustion temperature of the syngas the mixture quality between syngas and air at the flame front is a significant influencing variable for avoiding temperature peaks and thereby for minimizing thermal nitrous oxide formation.

The main elements of the syngases, in addition to carbon monoxide and hydrogen, are also inert components. The inert components involved are nitrogen and/or water vapor and where necessary also carbon dioxide. As a consequence of the low heating value, high volume flows of combustion gas must accordingly be introduced into the combustion chamber. The result of this is that far greater injector cross-sections are required for the combustion of low-calorific fuels such as syngases for example than with conventional high-calorific combustion gases.

The air mass flow introduced into the combustion chamber is typically swirled with the aid of an air swirl generator. The fuel is injected into this swirled air mass flow via one or more rows of circular holes arranged next to one another or behind one another.

To guarantee an adequate mixing of air and fuel a sufficient penetration depth of the individual jets of fuel into the air mass flow is necessary. Compared to high-calorific burner gases such as natural gas, correspondingly larger, free injection cross sections are required. The result of this is that the fuel jets disturb the sensitive air flow, which in the final analysis leads to a local detachment of the air flow in the feedback region of the fuel jets. The flowback regions forming within the burner are undesired and especially to be avoided at all costs for the combustion of highly-reactive syngas. In the extreme case these local flowback regions lead within the mixture zone of the burner to a flame blowback in the premix zone and thereby to damage to the burner.

The risk of flame blowback can be largely avoided by highly-reactive syngases being burned in diffusion mode. To realize low nitrous oxide emissions however heavy thinning with inert gases, preferably with steam, is necessary. In the case of a premixing combustion the formation of trail regions or hot gas flowback regions within the burner can be reduced by suitable shaping of the injection holes, but not basically avoided.

In EP 1 614 963 A1, for reducing the nitrous oxide emissions and for preventing flame blowback in the combustion of low-calorific fuels for the operation of a gas turbine, a method is proposed in which a low-calorific fuel is premixed with the air in stages.

In EP 1 614 967 A1 a further method for combustion of a low-calorific fuel for the operation of a gas turbine is proposed in which, within the framework of a pre-mixing, the low-calorific fuel is premixed with a low-calorific fuel-air mixture and a conversion of the low-calorific fuel-air mixture is avoided.

Specifically for preventing flame blowbacks, a gas turbine with an annular combustion chamber is proposed in EP 1 507 120 A1, in which a swirl grid is arranged in a combustion air inlet area around the entire circumference of the annular combustion chamber, whereby a higher flow speed of the incoming combustion air is achieved compared to individual air inlet areas each with a swirl grid. This gives a higher security against flame blowbacks and a lower tendency for the formation of combustion vibrations.

SUMMARY OF INVENTION

To guarantee a secure premixing operation, a flow detachment or a flowback region within the premix zone of the burner is to be avoided at all costs. At the least however potential flowback regions are to be designed such that no damage is caused to the burner. As a rule the flowback regions occur in zones close to the wall in the trail of the fuel gas jets.

In respect of nitrous oxide minimization the addition of inert mass flows as a thinning medium into the air mass flow or the fuel mass flow (quenching) is usual. The use of the leaner premix technology makes it possible to reduce the quantity of the quenching medium employed, which enhances the economy of the plant. However the lack of inerting then means that the fuel is highly reactive.

The object of the present invention is to provide an advantageous method for operating a premixing burner in which the formation of hot gas flowback regions is avoided. A further object of the present invention is to provide an advantageous premixing burner.

These objects are achieved by a method for operating a premixing burner as claimed in the claims and a premixing burner as claimed in the claims. The dependent claims contain further advantageous embodiments of the invention.

The inventive method relates to a premixing burner which comprises a premixing zone. An air mass flow and fuel are injected into the combustion chamber, in which case a potential hot gas flowback region can form. The inventive method is characterized in that a fluid containing no fuel is injected into the premixing zone downstream of the fuel injection.

By the local injection of for example cold air into the trail or flowback regions, the formation of said regions within the premixing zone of the burner is largely prevented. And least the fuel in these regions is quenched and cooled off to the extent that no reaction or no ignition of the fuel-air mixture within the premixing zone of the burner can occur. This makes a secure premixing operation of the burner possible.

In particular the fluid can be injected along the surface located in the potential hot gas flowback region of the premixing zone in the main direction of flow into the premixing zone. The injection of a fluid along the component surface in the main direction of flow prevents the actual formation of the hot gas flowback region and/or quenches and cools the fuel-air mixture at this location such that no ignition conditions obtain.

The fuel can especially be injected at right angles to the main flow direction of the air mass flow into the premixing zone, which is advantageous in respect of the basic mixing of air and fuel. Basically there is the option of injecting the fuel on the cone side and/or on the hub side into the premixing zone. Furthermore the fuel can be injected via at least one swirler vane into the premixing zone. The fuel concerned can especially be a syngas.

The fluid injected along the surface located in the potential hot gas flowback region into the premixing zone can for example be air or an inert gas. Gases with very low reaction capabilities, which are only involved in a few chemical reactions for example, are referred to as inert gases. In particular carbon dioxide, water vapor, nitrogen, but also all noble gases can be used as an inert gas. The use of an inert gas is especially suitable if ignition conditions for easily-ignitable fuels are to be avoided.

When air is used as a fluid injected into the premixing zone it is advantageous to use air of the air mass flow supplied to the premixing zone in any event. For example a proportion of 10% of the overall air fed to the premixing zone can be split off and injected into the latter along the surface of the premixing zone located in the potential hot gas flowback region. The proportion of air injected along the surface of the premixing zone located in the potential hot gas flowback region can be selected as required. The preferred level of the air to be used depends in such cases on the geometry of the premixing zone, on the speed of the air mass flow and on the speed of the injected fuel.

The inventive premixing burner has a premixing zone, an air swirl generator with an air inlet and one or more fuel nozzles. In such cases the fuel can be injected through the fuel nozzles into an air mass flow swirled by the air swirl generator in the premixing zone, in which case a potential hot gas flowback region can form. The inventive premixing burner is characterized in that the premixing zone surface in the potential hot gas flowback region has at least one opening through which a fluid can be injected into the premixing zone. In particular openings can be present that are arranged so that fluid can be injected in the main direction of flow of the burner along the surface of the premixing zone.

The local injection of a fluid into the potential hot gas flowback region largely avoids the formation of the hot gas flowback region within the premixing zone of the burner. At the least however the hot gas in the hot gas flowback region is quenched and cooled off such that no reaction in the form of an ignition of the air-gas mixture within the premixing zone of the burner can occur. This prevents flame blowbacks and reduces the nitrous oxide formation, but also allows a secure premixing operation of the burner.

Preferably the premixing zone surface in the hot gas flowback region features a number of openings. The opening or the openings can advantageously be connected via a fluid channel to the air supply leading to the air swirl generator so that a part of the air can be injected through the opening as a fluid into the combustion chamber.

The injection nozzles can be located on the cone side and/or on the hub side of the premixing zone. Advantageously the fuel nozzles are arranged in one or more rows lying behind one another downstream of the air swirl generator. This makes a graduated fuel injection possible. Furthermore the fuel nozzles and/or the openings can be located in the air swirl generator, preferably in at least one swirler vane.

The individual fuel nozzles can be embodied as round holes for example. A further option consists of designing the fuel nozzles such that the fuel can be injected at right angles to the main flow direction of the air mass flow into the combustion chamber, which promotes the premixing. Naturally the fuel can also be injected at any other given angle to the air mass flow. The fuel employed can especially involve a syngas.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features, characteristics and advantages of the present invention will be explained below on the basis of an exemplary embodiment which refers to the enclosed figures.

FIG. 1 shows a schematic diagram of a section of a part of the premixing burner.

FIG. 2 shows a schematic diagram of the flow conditions within the premixing burner depicted in FIG. 1.

FIG. 3 shows a schematic diagram of a section through a part of the inventive premixing burner.

FIG. 4 shows a schematic diagram of the flow conditions within the premixing burner depicted in FIG. 3.

FIG. 5 shows a schematic diagram of a section through a swirler vane.

DETAILED DESCRIPTION OF INVENTION

The invention will be explained below in greater detail with reference to FIGS. 1 to 5. FIG. 1 shows a schematic diagram of a section through a part of a conventional premixing burner 1. The premixing burner 1 includes elements such as a housing 7, a premixing zone 2, a swirl generator 10 and/or one or more fuel nozzles 11. The premixing zone is arranged radial-symmetrically around the central axis 12. The outer side of the premixing zone 2, viewed from the central axis 12, is referred to below as the cone side 3. The side of the premixing zone 2 facing towards a central axis 12 will be referred to below as the hub side 4.

An air mass flow 5 arrives at the swirl generator 10 via an air supply inlet 16. The air swirl generator 10 swirls the air mass flow 5 and directs this into the premixing zone 2. From there the air mass flow is forwarded in the main direction of flow 9 to the combustion chamber (not shown).

On the hub side 4 of the premixing zone 2 are located one or more fuel nozzles 11. Fuel 6 is directed in the present example through the fuel nozzles 11 at right angles to the main direction of flow 9 of the air mass flow 5 into the premixing zone 2. A hot gas flowback area 8 is now formed downstream towards the fuel nozzle 11 in the main direction of flow 9. Instead of a perpendicular injection to the main direction of flow 9 of the air mass flow 5, the fuel 6 can also be injected at any other given angle to the main direction of flow 9.

The flow direction of the injected fuel is indicated by arrow 6, the flow direction of the supplied air mass flow is indicated by arrow 5. The main direction of flow inside the premixing zone 2 is marked by arrows 9.

The flow conditions inside the premixing zone 2 are depicted in a schematic diagram in FIG. 2. FIG. 2 shows an overhead view of the fuel nozzles 11 from the inside of the premixing zone 2. The main direction of flow of the air mass flow flowing past the fuel nozzles is indicated by arrows 9. Hot gas flowback regions 8 now form downstream from the fuel nozzles 11 in the main direction of flow 9. The flow direction of the hot gas flowing back is indicated by the arrows 13.

FIG. 3 shows a schematic diagram of a section through a part of the inventive premixing burner 1. The basic structure and the principal functioning of the premixing burner 1 depicted in FIG. 3 essentially correspond to the premixing burner shown in connection with FIG. 1.

In addition to the premixing burner described in connection with FIG. 1, the inventive premixing burner features one or more fluid inlet openings 14 which are located downstream of the fuel nozzle or nozzles 11 in the main direction of flow 9. The fluid inlet openings 14 open out into the premixing zone 2. Through these fluid inlet openings in the present exemplary embodiment a fluid, for example air or an inert gas, can be injected in the main flow direction 9 into the premixing zone 2. The flow direction of the injected fluid is indicated by arrows 15. In this case it runs within the premixing zone 2 essentially in parallel to the main direction of flow 9. The injected fluid prevents the formation of a hot gas flowback region as occurs with the premixing learner described in conjunction with FIG. 1.

FIG. 4 depicts schematically the flow conditions inside the premixing zone 2 shown in FIG. 3.

An overhead view of the fuel nozzles 11 and the fluid inlet openings 14 viewed from the premixing zone 2 can be seen in FIG. 4. The main direction of flow of the air flowing from the swirl generator 10 in the direction of the fuel nozzles 11 and the fluid inlet openings 14 is indicated by arrows 9. The direction of flow of the fluid injected through the fluid openings 14 is indicated by arrows 15. The hot gas 13 is carried along in the main direction of flow 9 by the inflowing of fluid. A flowback of the hot gas 13 against the main direction of flow 9 is effectively prevented in this manner.

In the current exemplary embodiment the fluid injected by the fluid inlet openings 14 involves air which is connected via a fluid channel with the air mass flow 5 and is split off from the latter. It has proved useful in respect of avoiding the flowback of hot gas to introduce around 5% to 20%, preferably 10%, of the overall air supplied to the premixing zone 2 via the fluid inlet openings 14 into the premixing zone 2. Instead of air an inert gas, for example carbon dioxide, water vapor or nitrogen can be injected into the premixing zone via the fluid inlet openings 14. The injection of a noble gas is however basically also possible.

The fuel can optionally be injected at right angles to the main direction of flow 9 of the air mass flow 5 into the premixing zone 2, as described in conjunction with FIG. 1 and FIG. 3, or the fuel can be injected at any given angle to the main direction of flow 9 of the air mass flow into the premixing zone 2. Basically the fuel nozzles and 11 can be located both on the cone side 3 and also on the hub side 4 of the premixing zone 2 or in the swirler vanes 17. In the event of the fuel nozzles 11 being located on the cone side 3 of the premixing zone 2, it is advantageous to also place the fluid inlet openings 14 correspondingly on the cone side 3. The fluid inlet openings 14 should then again be located in the main direction of flow 9 downstream to the fuel nozzles and make it possible to inject the fluid in the main direction of flow 9.

The fuel nozzles 11 can be arranged in one or more rows line behind one another downstream of the air swirl generator 10. They can advantageously be embodied as round holes. The fuel injected through them can especially involve a syngas.

A further embodiment of variant of the invention is described below in which the fuel 6 and the fluid 15 containing no fuel is injected into the premixing zone via swirler vanes 17. FIG. 5 shows a schematic diagram of a section through a swirler vane 17. The swirler vane 17 has a fuel flow channel 18 within it and a fluid flow channel 19 located downstream to it in the direction of the main flow 9.

The fuel 6 is injected via the fuel flow channel 18 through fuel nozzles 11 from the swirler vane 17 into the premixing zone 2. The fluid 15, which preferably involves an inert gas, is injected via the fluid flow channel 19 through fluid inlet openings 20, 21, 22 into the premixing zone 2. In this case the fluid inlet openings 20, 21, 22 are located in the main direction of flow 9 downstream from the fuel nozzles 11.

In the present embodiment variant a part of the fluid 15 is injected through fluid inlet openings 20 which are arranged downstream next to the fuel nozzles 11, essentially against the main direction of flow 9 into the premixing zone 2. By fluid inlet openings 21 arranged further downstream next to the fluid inlet openings 20 a part of the fluid 15 is injected almost at right angles to the main direction of flow 9 into the premixing zone 2. Further fluid inlet openings 22 are arranged downstream next to the fluid inlet openings 21, through which a part of the fluid 15 is injected essentially in the main direction of flow 9 into the premixing zone 2.

The described arrangement of the fluid inlet openings 20, 21, 22 avoids any hot gas flowback region arising downstream from the fuel nozzles 11 and thus makes possible a safe premixing operation of the burner. 

1.-18. (canceled)
 19. A method for operating a premixing burner including a premixing zone, the method comprising: injecting an air mass flow and fuel into the premixing zone wherein a hot gas flowback region may form; and injecting a fluid containing no fuel into the premixing zone downstream from the fuel injection.
 20. The method as claimed in claim 19, wherein the fluid is injected along a surface of the premixing zone located in the potential hot gas flowback region, and wherein the fluid is injected in a main direction of air mass flow into the premixing zone.
 21. The method as claimed in claim 19, wherein the fuel is injected at right angles to the main direction of air mass flow into the premixing zone.
 22. The method as claimed in claim 19, wherein the premixing zone comprises a cone side and a hub side, and wherein the fuel is injected into the premixing zone on the cone side and/or on the hub side.
 23. The method as claimed in claim 19, wherein the fuel is injected into the premixing zone via a swirler vane.
 24. The method as claimed in claim 19, wherein the fuel is a syngas.
 25. The method as claimed in claim 19, wherein the fluid is air.
 26. The method as claimed in claim 25, wherein a proportion of 10 percent of an overall air supplied to the premixing zone is injected along the surface of the premixing zone located in the hot gas flowback region.
 27. The method as claimed in claim 19, wherein the fluid is an inert gas.
 28. The method as claimed in claim 27, wherein the inert gas is a noble gas, carbon dioxide, water vapor or nitrogen.
 29. A premixing burner, comprising: a premixing zone; an air swirl generator including an air inlet; and a fuel nozzle, wherein a fuel may be injected through the fuel nozzle into an air mass flow swirled by the air swirl generator in the premixing zone where a hot gas flowback region may form, and wherein a surface of the premixing burner in the potential hot gas flowback region includes an opening through which a fluid may be injected into the premixing zone.
 30. The premixing burner as claimed in claim 29, wherein the opening is connected in such a way via a fluid channel to the air inlet leading to the air swirl generator that a portion of the air mass flow may be injected through the opening as the fluid into the premixing zone.
 31. The premixing burner as claimed in claim 29, wherein the premixing zone comprises a cone side and a hub side, and wherein the premixing zone also comprises a plurality of fuel nozzles on the cone side and/or the hub side of the premixing zone.
 32. The premixing burner as claimed in claim 29, wherein the plurality of fuel nozzles are arranged in one or more rows lying behind one another downstream of the air swirl generator.
 33. The premixing burner as claimed in claim 29, wherein the plurality of fuel nozzles and/or a plurality of openings are located in the air swirl generator.
 34. The premixing burner as claimed in claim 33, wherein the fuel is injected via a fluid flow channel through the plurality of openings into the premixing zone, and wherein the plurality of openings are located in a main direction of air mass flow downstream from the plurality of fuel nozzles.
 35. The premixing burner as claimed in claim 29, wherein the plurality of fuel nozzles are embodied as a plurality of round holes.
 36. The premixing burner as claimed in claim 29, wherein the plurality of fuel nozzles are designed so that the fuel may be injected at right angles to the main direction of air mass flow into the premixing zone.
 37. The premixing burner as claimed in claim 29, wherein the fuel is a syngas.
 38. The premixing burner as claimed in claim 29, wherein the fluid may be injected into the premixing zone through a plurality of openings in the main direction of air mass flow, and wherein the fluid is injected into the premixing zone along the surface of the premixing zone. 